Braking control device for vehicle

ABSTRACT

Brake fluid inside a first wheel cylinder is pressurized by using a first pressure-regulating mechanism and brake fluid inside a second wheel cylinder is pressurized by using a second pressure-regulating mechanism. If a determination means determines that the first pressure-regulating mechanism action is in an unsuitable state and the second pressure-regulating mechanism action is in a suitable state, the control means pressurizes the brake fluid inside the first wheel cylinder by using a master cylinder and pressurizes the brake fluid inside the second wheel cylinder by using the second pressure-regulating mechanism, when an operation volume is less than a value. When the operation volume has reached the value, the control means pressurizes the brake fluid inside the first and second wheel cylinders by using the second pressure-regulating mechanism.

TECHNICAL FIELD

The present invention relates to a braking control device for a vehicle.

BACKGROUND ART

Patent Literature 1 describes “providing Pc cut valves that cut outputlines of pressure controlling valves and a connecting valve thatconnects left and right wheel cylinders, and in an event of failure, thePc cut valve in a failed system is closed and the connecting valve isopened to send outputs from the pressure controlling valve in a normalsystem to the wheel cylinder in the failed system”.

Patent Literature 2 describes, an electrically driven fluid pressureoutput part which is “provided with a cylinder body having its distalend side formed as a closed end to have a bottomed cylinder shape, aguide cylinder coaxially connected to a rear end of the cylinder body, asupport cylinder coaxially connected to the guide cylinder, a connectingcylinder coaxially connected to the support cylinder, a motor includingan encoder and being coaxially coupled to the connecting cylinder, apiston slidably fitted in the cylinder body and forming a pressurechamber with the closed end of the cylinder body, a cylindrical nutmember arranged in the guide cylinder by being prohibited to rotateabout an axis line, and coaxially connected to a rear end of the piston,and a rotation shaft coupled to the nut member via a ball screw andconnected to an output shaft of the motor via an Oldham's joint (seeFIG. 2 of Patent Literature 2)”.

Application of the technical contents described in Patent Literature 1to the device described in Patent Literature 2 will be assumed. In thedevice of the Patent Literature 2, since brake fluid is pushed out fromthe cylinder by the piston, there is a limit to an amount of the brakefluid that can be discharged from the cylinder. Due to this, when thebrake fluid is to be supplied from a brake system (fluid path) in asuitable state to a wheel cylinder in a brake system (fluid path) in anunsuitable state, a state in which the piston fully strokes, and thebrake fluid can no further be discharged from the cylinder may occur. Aso-called piston bottoming occurs, and insufficiency in a brake fluidvolume may occur.

CITATIONS LIST Patent Literature

Patent Literature 1: JP H11-255090 A

Patent Literature 2: JP H04-362454 A

SUMMARY OF INVENTION Technical Problems

An aim of the present invention is to provide a braking control devicefor a vehicle in which pressures of wheel cylinders are regulated usingcontrol cylinders, that can suitably supply brake fluid withoutoccurrences of fluid volume insufficiencies of the brake fluid.

Solutions to Problems

A braking control device for a vehicle according to the presentinvention is provided with: a master cylinder (MCL) configured to bedriven by a brake operation member (BP) of the vehicle; a first wheelcylinder (WC1) configured to apply brake torque to one of left and rightfront wheels (WHfl, WHfr) of the vehicle; a second wheel cylinder (WC2)configured to apply brake torque to the other of the left and rightfront wheels (WHfl, WHfr) of the vehicle; a first fluid path (H1)connecting the master cylinder (MCL) and the first wheel cylinder (WC1);a second fluid path (H2) connecting the master cylinder (MCL) and thesecond wheel cylinder (WC2); a first opening/closing means (VM1)provided on the first fluid path (H1), and configured to selectivelyproduce a flowing state and an interrupted state of brake fluid betweenthe master cylinder (MCL) and the first wheel cylinder (WC1); a secondopening/closing means (VM2) provided on the second fluid path (H2), andconfigured to selectively produce a flowing state and an interruptedstate of brake fluid between the master cylinder (MCL) and the secondwheel cylinder (WC2); a third opening/closing means (VRN) provided on aconnection fluid path (HRN) connecting the first wheel cylinder (WC1)and the second wheel cylinder (WC2), and configured to selectivelyproduce a flowing state and an interrupted state of brake fluid betweenthe first wheel cylinder (WC1) and the second wheel cylinder (WC2); anoperation volume acquiring means (BPA) configured to acquire anoperation volume (Bpa) of the brake operation member (BP); a firstpressure-regulating mechanism (CA1) connected to the first fluid path(H1) between the first opening/closing means (VM1) and the first wheelcylinder (WC1), and configured to pressurize the brake fluid in thefirst wheel cylinder (WC1); a second pressure-regulating mechanism (CA2)connected to the second fluid path (H2) between the secondopening/closing means (VM2) and the second wheel cylinder (WC2), andconfigured to pressurize the brake fluid in the second wheel cylinder(WC2); a control means (CTL) configured to control the first, second,and third opening/closing means (VM1, VM2, VRN) and the first and secondpressure-regulating mechanisms (CA1, CA2) based on the operation volume(Bpa); and a determination means (HNT) configured to determine whetheractuation of the first and second pressure-regulating mechanisms (CA1,CA2) is in a suitable state or in an unsuitable state.

The characteristic feature of the braking control device for a vehicleaccording to the present invention lies in that, in a case where thedetermination means (HNT) determines that the actuation of the first andsecond pressure-regulating mechanisms (CA1, CA2) is in the suitablestate, the control means (CTL) causes the first, second, and thirdopening/closing means (VM1, VM2, VRN) to be in the interrupted state,and causes the brake fluid in the first wheel cylinder (WC1) to bepressurized by the first pressure-regulating mechanism (CA1) and thebrake fluid in the second wheel cylinder (WC2) to be pressurized by thesecond pressure-regulating mechanism (CA2), and in a case where thedetermination means (HNT) determines that the actuation of the firstpressure-regulating mechanism (CA1) is in the unsuitable state and theactuation of the second pressure-regulating mechanism (CA2) is in thesuitable state, the control means causes the first opening/closing means(VM1) to be in the flowing state and the second and thirdopening/closing means VM2, VRN) to be in the interrupted state, andcauses the brake fluid in the first wheel cylinder (WC1) to bepressurized by the master cylinder (MCL) and the brake fluid in thesecond wheel cylinder (WC2) to be pressurized by the secondpressure-regulating mechanism (CA2) when the operation volume (Bpa) isless than a prescribed value (bpk), and causes the first opening/closingmeans (VM1) to be in the interrupted state and the third opening/closingmeans (VRN) to be in the flowing state, and causes the brake fluid inthe first and second wheel cylinders(WC1, WC2) to be pressurized by thesecond pressure-regulating mechanism (CA2) when the operation volume(Bpa) is equal to or more than the prescribed value (bpk).

The characteristic feature of the braking control device for a vehicleaccording to the present invention lies in that, in a case where thedetermination means (HNT) determines that the actuation of the first andsecond pressure-regulating mechanisms (CA1, CA2) is in the suitablestate, the control means (CTL) causes the first, second, and thirdopening/closing means (VM1, VM2, VRN) to be in the interrupted state,and causes the brake fluid in the first wheel cylinder (WC1) to bepressurized by the first pressure-regulating mechanism (CA1) and thebrake fluid in the second wheel cylinder (WC2) to be pressurized by thesecond pressure-regulating mechanism (CA2), and in a case where thedetermination means (HNT) determines that the actuation of the firstpressure-regulating mechanism (CA1) is in the unsuitable state and theactuation of the second pressure-regulating mechanism (CA2) is in thesuitable state, the control means causes the first and secondopening/closing means (VM1, VM2) to be in the flowing state, and causesthe brake fluid in the first and second wheel cylinders (WC1, WC2) to bepressurized by the master cylinder (MCL) when the operation volume (Bpa)is less than a prescribed value (bpk), and causes the first and secondopening/closing means (VM1, VM2) to be in the interrupted state and thethird opening/closing means (VRN) to be in the flowing state, and causesthe brake fluid in the first and second wheel cylinders(WC1, WC2) to bepressurized by the second pressure-regulating mechanism (CA2) when theoperation volume (Bpa) is equal to or more than the prescribed value(bpk).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall configurational diagram showing a first embodimentof a braking control device for a vehicle according to the presentinvention.

FIG. 2 is a partial cross-sectional diagram for explaining apressure-regulating mechanism.

FIG. 3 is a functional block diagram for explaining a calculationprocess by an electronic control unit.

FIG. 4 is a circuitry diagram for explaining an electric motor drivingmeans.

FIG. 5 is a flow chart for explaining a first example of a brake fluidinitial filling control.

FIG. 6 is a characteristic diagram for explaining workings and effectsof the first example of the brake fluid initial filling control.

FIG. 7 is a flow chart for explaining a second example of the brakefluid initial filling control.

FIG. 8 is a characteristic diagram for explaining workings and effectsof the second example of the brake fluid initial filling control.

FIG. 9 is an overall configurational diagram showing a second embodimentof the braking control device for a vehicle according to the presentinvention.

FIG. 10 is a schematic diagram for explaining an electric braking meansfor rear wheels.

DESCRIPTION OF EMBODIMENTS

Embodiments of a braking control device for a vehicle according to thepresent invention will be described with reference to the drawings. Inthe description below, the added letters (such as “fl”) that are addedto respective reference signs indicate the respective reference signsrelate to which wheels. Specifically, “fl” indicates a left front wheel,“fr” indicates a right front wheel, “rl” indicates a left rear wheel,and “rr” indicates a right rear wheel. For example, the respective wheelcylinders will be denoted as a left front wheel cylinder WCfl, a rightfront wheel cylinder WCfr, a left rear wheel cylinder WCrl, and a rightrear wheel cylinder WCrr.

Further, the numbers (“1” or “2”) added to the respective signs indicatetwo fluid paths (fluid pressure systems) are connected to which one ofthe left front wheel cylinder WCfl and the right front wheel cylinderWCfr. Specifically, a system connected to the left front wheel cylinderWCfl (hereafter termed a first system) is expressed using “1”, and asystem connected to the right front wheel cylinder WCfr (hereaftertermed a second system) is expressed using “2”. For example, a firstpressure-regulating mechanism CA1 is for adjusting fluid pressure of theleft front wheel cylinder WCfl (corresponding to a first wheel cylinderWC1) and a second pressure-regulating mechanism CA2 is for adjustingfluid pressure of the right front wheel cylinder WCfr (corresponding toa second wheel cylinder WC2). In each of the constituent features,configurations of the first system (first fluid path) and configurationsof the second system (second fluid path) are same. Due to this, thedescription hereinbelow will be given mainly for the constituentfeatures of the first system.

<First Embodiment of Braking Control Device According to the PresentInvention>

As shown in an overview configurational diagram of FIG. 1, a vehicleprovided with a braking control device according to the presentinvention is provided with a brake operation member BP, an operationvolume acquiring means BPA, an electronic control unit ECU, a tandemmaster cylinder MCL, a stroke simulator SSM, electromagnetic valves VM1,VM2, VSM, VRN, and first and second pressure-regulating mechanisms CA1,CA2. Further, the wheels WHfl, WCfr, WHrl, WHrr are respectivelyprovided with brake calipers CPfl, CPfr, CPrl, CPrr, wheel cylindersWCfl, WCfr, WCrl, WCrr, and rotary members (for example, brake disks)KTfl, KTfr, KTrl, KTrr.

A brake operation member (for example, brake pedal) BP is a member to beoperated by a driver to decelerate the vehicle. When the brake operationmember BP is operated, brake torque of the wheels (WHfl, etc.) isadjusted, and braking force is generated in the wheels. Specifically,the rotary member (for example, a brake disk) is fixed to each wheel ofthe vehicle. The brake calipers (CPfl, etc.) are arranged to interposethe rotary members (KTfl, etc.) therein. Further, the wheel cylinders(WCfl, etc.) are provided on the brake calipers. When pressure of thebrake fluid inside the wheel cylinders is increases, frictional members(for example, brake pads) are pressed against the rotary members.Frictional force generated upon this pressing generates the brake torquein the wheel.

The brake operation member BP is provided with an operation volumeacquiring means BPA. The operation volume acquiring means BPA acquires(detects) the driver's operation volume (braking operation volume) Bpaof the brake operation member BP. Specifically, as the operation volumeacquiring means BPA, at least one of first and second master cylinderfluid pressure acquiring means (pressure sensors) PM1, PM2 that acquirepressure of the tandem master cylinder MCL, an operation displacementacquiring means (stroke sensor) SBP that acquires an operationaldisplacement Sbp of the brake operation member BP, and an operationalforce acquiring means (tread force sensor) FBP (not shown) that acquiresan operational force Fbp of the brake operation member BP may beemployed. In other words, the operation volume acquiring means BPA is acollective term for the master cylinder fluid pressure acquiring means,the operation displacement acquiring means, and the operational forceacquiring means. The braking operation volume Bpa is determined based onat least one of first and second master cylinder fluid pressures Pm1,Pm2, the operational displacement Sbp of the brake operation member, andthe operational force Fbp of the brake operation member. Here, one ofthe first and second master cylinder fluid pressure acquiring means PM1,PM2 may be omitted.

The braking operation volume Bpa (Pm1, Sbp, etc.) is inputted to theelectronic control unit ECU. Power is supplied to the electronic controlunit ECU by a rechargeable battery (battery) BAT and a generator(alternator) ALT. The first and second pressure-regulating mechanismsCA1, CA2 and the electromagnetic valves VM1, VM2, VSM, VRN arecontrolled by the electronic control unit ECU based on the brakingoperation volume Bpa. Specifically, the electronic control unit ECU isprogrammed with a control algorithm for controlling electric motors MT1,MT2 and the electromagnetic valves VM1, VM2, VSM, VRN.

First and second control cylinder fluid pressures Pc1, Pc2 acquired byfirst and second control cylinder fluid pressure acquiring means PC1,PC2 are inputted to the electronic control unit ECU. In the electroniccontrol unit ECU, driving signals It1, It2 for the electric motors MT1,MT2 and instruction signals Vm1, Vm2, Vsm, Vrn for the electromagneticvalves VM1, VM2, VSM, VRN are calculated, and the electric motors andthe electromagnetic valves are controlled based on these signals.

The tandem master cylinder (which may simply be termed a mastercylinder) MCL converts the operational force (brake pedal tread force)on the brake operation member BP to a fluid pressure, and pressurizesand feeds brake fluid to the wheel cylinders of the respective wheels.Specifically, first and second master cylinder chambers Rm1, Rm2 definedby two master pistons MP1, MP2 are formed in the master cylinder MCL,and these are connected to the wheel cylinders of the respective wheelsvia fluid paths (pipes). In a case where the brake operation member BPis not operated, the master cylinder chambers Rm1, Rm2 are in a flowingstate with a master reservoir RSV, and the fluid pressure inside themaster cylinder is at atmospheric pressure.

<Fluid Paths of Two Systems (Diagonal Piping)>

Paths through which the brake fluid (brake fluid) moves among the tandemmaster cylinder MCL and the four-wheel cylinders WCfl, WCfr, WCrl, WCrr(fluid paths) are configured of two systems. In one of the systems(first fluid path H1), the first fluid pressure chamber Rm1 of themaster cylinder MCL and the wheel cylinders WCfl (corresponding to firstwheel cylinder WC1), WCrr are connected. In the other of the systems(second fluid path H2), the second fluid pressure chamber Rm2 of themaster cylinder MCL and the wheel cylinders WCfr (corresponding tosecond wheel cylinder WC2), WCrl are connected. A configuration of aso-called diagonal piping (which may also be termed X piping) isemployed. Since a configuration of the first fluid path (first brakepiping) H1 and a configuration of the second fluid path (second brakepiping) H2 are basically the same, the configuration of the first fluidpath H1 will be described.

A first master cylinder shutoff valve VM1 is provided (interposed) onthe fluid path H1 connecting the first fluid pressure chamber (firstmaster cylinder chamber) Rm1 of the master cylinder MCL and the wheelcylinders WCfl, WCrr. The first master cylinder shutoff valve VM1 is atwo-position electromagnetic valve having an open position and a closedposition. In a case where the first master cylinder shutoff valve VM1 isin the open position, the first master cylinder chamber Rm1 and the leftfront wheel cylinder WCfl are in a flowing state, and in a case whereVM1 is in the closed position, Rm1 and WCfl are in an interrupted state(non-flowing state). As the first master cylinder shutoff valve VM1, anormally-open electromagnetic valve (NO valve) may be employed.

A first fluid pressure unit HU1 is interposed on a fluid path HW1 (beinga part of H1) connecting the first master cylinder shutoff valve VM1 andthe wheel cylinders WCfl, WCrr. Here, the first fluid path (first brakepiping) is configured by a fluid path (piping) HM1 and the fluid path(piping) HW1. The first fluid pressure unit HU1 is configured of abooster valve and a reducing valve, and controls fluid pressures of thewheel cylinders WCfl, WCrr independently upon executing anti-skiddingcontrol, vehicle stabilization control, and the like.

In the fluid path HW1, the first pressure-regulating mechanism CA1 andthe first control cylinder fluid pressure acquiring means PC1 areprovided between the first master cylinder shutoff valve VM1 and thefirst fluid pressure unit HU1. The first pressure-regulating mechanismCA1 is configured of a first control cylinder SC1 and the first electricmotor MT1. In the case where the first master cylinder shutoff valve VM1is in the closed position, it adjusts (boosts or reduces) the fluidpressures of the wheel cylinders WCfl, WCrr. The fluid pressure Pc1adjusted by the first pressure-regulating mechanism CA1 is acquired(detected) by the first control cylinder fluid pressure acquiring meansPC1.

The first master cylinder fluid pressure acquiring means PM1 is providedon the fluid path HM1 (which is a part of H1) connecting the firstmaster cylinder chamber Rm1 and the first master cylinder shutoff valveVM1. The master cylinder fluid pressure Pm1 generated by the mastercylinder MCL is acquired (detected) by the first master cylinder fluidpressure acquiring means PM1.

The stroke simulator (which may simply be termed a simulator) SSM isprovided for causing the brake operation member BP to generate theoperational force. The simulator shutoff valve VSM is provided on thefluid path HSM connecting the first fluid pressure chamber Rm1 of themaster cylinder MCL and the simulator SSM. The simulator shutoff valveVSM is a two-position electromagnetic valve having an open position anda closed position. In a case where the simulator shutoff valve VSM is inthe open position, the first master cylinder chamber Rm1 and thesimulator SSM are in a flowing state, and in a case where VSM is in theclosed position, Rm1 and SSM are in an interrupted state (non-flowingstate). As the simulator shutoff valve VSM, a normally-closedelectromagnetic valve (NC valve) may be employed.

A piston and an elastic body (for example, a compression spring) areprovided inside the simulator SSM. The brake fluid is moved from themaster cylinder MCL (Rm1) to the simulator SSM, and the inflowing brakefluid presses the piston. The piston is biased by the elastic bodytoward a direction of inhibiting the inflow of the brake fluid. Theelastic body creates the operational force (for example, brake pedaltread force) for the case where the brake operation member BP isoperated.

Next, the configuration of the second fluid path H2 will be brieflydescribed. As aforementioned, the configuration of the first fluid pathH1 and the configuration of the second fluid path H2 are basically thesame. Thus, Rm1 corresponds to Rm2, WHfl (WC1) corresponds to WCfr(WC2), WCrr corresponds to WCrl, HM1 corresponds to HM2, HW1 correspondsto HW2, HU1 corresponds to HU2, VM1 corresponds to VM2, CA1 correspondsto CA2, PM1 corresponds to PM2, and PC1 corresponds to PC2,respectively. That is, a description that replaced “first” to “second”and “1” at the end of the signs to “2” in the description of theconstituent features of the first fluid path H1 corresponds to thedescription of the constituent features of the second fluid path H2.Here, the stroke simulator is omitted in the constituent features of thesecond fluid path H2; however, an independent stroke simulator may beprovided in the second fluid path H2 as well.

Further, a connection fluid path HRN (H3) connecting the first fluidpath H1 and the second fluid path H2 is provided. That is, the firstpressure-regulating mechanism CA1 and the second pressure-regulatingmechanism CA2 are hydrodynamically connected by the connection fluidpath HRN. A connection valve VRN (corresponding to third opening/closingmeans) is provided on the connection fluid path HRN. The connectionvalve VRN is a normally-closed, two-position electromagnetic valve. In acase where the connection valve VRN is in an open position, the firstpressure-regulating mechanism CA1 (that is, the first wheel cylinderWCfl, etc.) and the second pressure-regulating mechanism CA2 (that is,the second wheel cylinder WCfr, etc.) are in a flowing state. On theother hand, in a case where the connection valve VRN is in a closedposition, the first pressure-regulating mechanism CA1 and the secondpressure-regulating mechanism CA2 are in a non-flowing state.

<Pressure-Regulating Mechanism>

Details of the pressure-regulating mechanism will be described withreference to a partial cross-sectional diagram of FIG. 2. Since thefirst pressure-regulating mechanism CA1 (especially the configurationcorresponding to the left front wheel WHfl) and the secondpressure-regulating mechanism CA2 (especially the configurationcorresponding to the right front wheel WHfr) have a same configuration,the first pressure-regulating mechanism CA1 will be described. For thedescription of the second pressure-regulating mechanism CA2, it may beexplained by replacing “first” to “second”, added letter “1” to addedletter “2”, added letter “fl” to added letter “fr”, and added letter“rr” to added letter “rl”.

The first pressure-regulating mechanism CA1 is provided on the firstfluid path H1 on an opposite side from the master cylinder MCL withrespect to the first master cylinder shutoff valve (electromagneticvalve) VM1 (that is, on a wheel cylinder WCfl side). Thus, in the casewhere the electromagnetic valve VM1 is in the closed position(interrupted state), the fluid pressure of the wheel cylinder WCfl, etc.is adjusted by input and output of the brake fluid from the firstpressure-regulating mechanism CA1.

The first pressure-regulating mechanism CA1 is configured of the firstelectric motor MT1, a reduction gear GSK, a rotation-linear motionconverting mechanism (screw member) NJB, a pressing member PSH, thefirst control cylinder SC1, a first control piston PS1, and a returnspring SPR.

The first electric motor MT1 is a power source for the firstpressure-regulating mechanism CA1 to adjust (boost, reduce, etc.) thepressures of the brake fluid in the wheel cylinders. The first electricmotor MT1 is driven by the electronic control unit ECU. As the firstelectric motor MT1, a brushless DC motor may be employed.

The reduction gear GSK is configured of a small diameter gear SKH and alarge diameter gear DKH. Here, a number of teeth of the large diametergear DKH is greater than a number of teeth of the small diameter gearSKH. Thus, rotational force of the electric motor MT1 is reduced by thereduction gear GSK and is transmitted to the screw member NJB.Specifically, the small diameter gear SKH is fixed to an output shaftJmt of the electric motor MT1. The large diameter gear DKH is meshedwith the small diameter gear SKH, and the large diameter gear DKH and abolt member BLT of the screw member NJB are fixed so that a rotationshaft Jsc of the large diameter gear DKH coincides with a rotation shaftof the bolt member BLT. That is, in the reduction gear GSK, therotational force from the electric motor MT1 is inputted to the smalldiameter gear SKH, is reduced, and then outputted from the largediameter gear DKH to the screw member NJB.

The screw member NJB converts the rotational force of the reduction gearGSK to a linear motion force Fs of the pressing member PSH. A nut memberNUT is fixed to the pressing member PSH. The bolt member BLT of thescrew member NJB is fixed coaxially with the large diameter gear DKH.Rotational motion of the nut member NUT is constrained by a key memberKYB, so the nut member NUT (that is, the pressing member PSH) engaged bythread with the bolt member BLT is moved in a direction of the rotationshaft of the large diameter gear DKH by rotation of DKH. That is, thescrew member NJB converts the rotational force of the first electricmotor MT1 to the linear motion force Fs of the pressing member PSH.

The first control piston PS1 is moved by the pressing member PSH. Thefirst control piston PS1 is inserted into an inner hole IH1 (first innerhole) of the first control cylinder SC1, and a combination of a pistonand cylinder is thereby formed. Specifically, a sealing member GSC isprovided on an outer circumference of the first control piston PS1, andfluid tightness with the inner hole (inner wall) of the first controlcylinder SC1 is ensured. That is, a fluid chamber (control cylinderchamber) Rsc defined by the first control cylinder SC1 and the firstcontrol piston PS1 is thereby formed. The control cylinder chamber Rscis connected to the fluid path (piping) HW1 via a port Ksc. With thefirst control piston PS1 being moved in an axial direction (center axisJsc), a volume of the control cylinder chamber Rsc thereby changes. Atthis occasion, since the electromagnetic valve VM1 is in the closedposition, the brake fluid is not moved to a direction of the mastercylinder MCL (that is, the master cylinder chamber Rm1), but is movedtoward the wheel cylinder WCfl.

The first pressure-regulating mechanism CA1 is provided with the returnspring (elastic body) SPR. When power conduction to the first electricmotor MT1 is stopped, the first control piston PS1 is returned to aninitial position (position corresponding to the brake fluid pressurebeing zero) by the return spring SPR. Specifically, a stopper portionStp is provided inside the first control cylinder SC1, and in a casewhere the output of the first electric motor MT1 is zero, the firstcontrol piston PS1 is pressed to a position where it makes contact withthe stopper portion Stp (initial position) by the return spring SPR.

The brake caliper CPfl is of a floating type, and the wheel cylinderWCfl is provided therein. A wheel piston PWC is inserted to an innerhole of the wheel cylinder WCfl, and a combination of a piston and acylinder is thereby formed. A sealing member GWC is provided on an outercircumference of the wheel piston PWC, and fluid tightness between GWCand the inner hole (inner wall) of the wheel cylinder WCfl is achieved.That is, the sealing member GWC of the wheel cylinder forms a fluidchamber (wheel cylinder chamber) Rwc defined by the wheel cylinder WCfland the wheel piston PWC. The wheel piston PWC is connected to thefrictional member MSB, and is configured capable of pressing MSB.

The wheel cylinder chamber Rwc formed by a combination of the wheelpiston PWC and the wheel cylinder WCfl is filled with the brake fluid.Further, the fluid chamber Rwc is connected to the fluid path (piping)HW1 via the port Kwc. Accordingly, when the first control piston PS1 isreciprocated by the first electric motor MT1 in a direction of a centeraxis Jsc and a volume of the control cylinder chamber Rsc is increasedor decreased, a pressure change in the brake fluid in the wheel cylinderchamber Rwc occurs due to inflow or outflow of the brake fluid to thewheel cylinder chamber Rwc. Due to this, the force by which thefrictional member (for example, brake pad) MSB presses the rotary member(for example, brake disk) KTfl is adjusted, and the brake torque of thewheel WHfl is thereby controlled.

Specifically, when the first electric motor MT1 is rotary driven in aforward direction Fwd, the first control piston PS1 is moved to decreasea volume of the control cylinder chamber Rsc (movement to left directionin the drawings), and the brake fluid is moved from the first controlcylinder SC1 to the first wheel cylinder WCfl. Due to this, a volume ofthe wheel cylinder chamber Rwc is increased, the pressing force of thefrictional member MSB onto the rotary member KTfl increases, and thebrake torque of the wheel WHfl increases. On the other hand, when thefirst electric motor MT1 is rotary driven in a reverse direction Rvs,the first control piston PS1 is moved to increase the volume of thecontrol cylinder chamber Rsc (movement to right direction in thedrawings), and the brake fluid is moved from the first wheel cylinderWCfl to the first control cylinder SC1. Due to this, the volume of thewheel cylinder chamber Rwc is decreased, the pressing force of thefrictional member MSB onto the rotary member KTfl decreases, and thebrake torque of the wheel WHfl decreases.

In order to control the brake fluid pressures independently for eachwheel in the anti-skidding control, the vehicle stabilization control,and the like, the first fluid pressure unit HU1 is provided between thefirst pressure-regulating mechanism CA1 (that is, the first controlcylinder SC1) and the wheel cylinders WCfl, WCrr. The first fluidpressure unit HU1 is configured of a combination of a booster valve(electromagnetic valve) and a reducing valve (electromagnetic valve). Ina case of retaining the wheel cylinder fluid pressure, the booster valveand the reducing valve are brought to a closed position, and inflow ofthe brake fluid from the first pressure-regulating mechanism CA1 to thewheel cylinder is inhibited. In a case of decreasing the wheel cylinderfluid pressure, the reducing valve is brought to an open position in astate of having the booster valve in the closed position, and the brakefluid is returned to the master reservoir RSV. Further, in a case ofincreasing the wheel cylinder fluid pressure, the reducing valve isbrought to the closed position and the booster valve is brought to anopen position, and the brake fluid flows into the wheel cylinder fromthe first pressure-regulating mechanism CA1.

In the first fluid path (brake piping) HW1, the first control cylinderfluid pressure acquiring means (pressure sensor) PC1 is provided betweenthe first master cylinder shutoff valve VM1 and the first fluid pressureunit HU1. The fluid pressure (first control cylinder fluid pressure) Pc1outputted by the first control cylinder SC1 is acquired (detected) bythe first fluid pressure acquiring means PC1.

In between the first master cylinder shutoff valve VM1 and the firstfluid pressure unit HU1, the first fluid path (brake piping) HW1 isconnected to the second fluid path (brake piping) HW2 via the connectionfluid path (brake piping) HRN. The connection valve VRN is interposed onthe connection fluid path HRN. In a state where the connection valve VRNis in the open position, the connection fluid path HRN is in a flowingstate, and when it is in the closed position, the connection fluid pathHRN is in an interrupted state. Thus, the hydrodynamic connection(connection/no-connection) of the first pressure-regulating mechanismCA1 and the second pressure-regulating mechanism CA2 is switched byopening and closing the connection valve VRN.

<Process in Electronic Control Unit ECU>

Next, a process in the electronic control unit ECU will be describedwith reference to a functional block diagram of FIG. 3. The electroniccontrol unit ECU receives power supply from the power source(rechargeable battery BAT, generator ALT), and controls the first andsecond electric motors MT1, MT2, the stroke simulator shutoff valve(electromagnetic valve) VSM, the first and second master cylindershutoff valves (electromagnetic valves) VM1, VM2, and the connectionvalve (electromagnetic valve) VRN. The process in the electronic controlunit ECU is configured by a suitability determining part (suitabilitydetermining block) HNT, a motor controlling part CMT, and anelectromagnetic valve controlling part CSL. Here, the motor controllingpart CMT and the electromagnetic valve controlling part CSL are termed“control means CTL”.

<<Suitability Determining Part (Suitability Determining Block) HNT>>

The suitability determining block HNT (corresponding to determinationmeans) is a calculation algorithm, and is programmed in a microcomputerin the electronic control unit ECU. The suitability determining blockHNT determines suitability of an actuation state of the overall system,including the suitability of the actuation states of the first andsecond electric motors MT1, MT2. The suitability of the actuation statesof the first and second electric motors MT1, MT2 is determined based onat least one of power supply states (for example, supplied voltages) ofthe electric motors MT1, MT2, the actuation state of the electroniccontrol unit ECU that drives the electric motors MT1, MT2, and theactuation states of the acquiring means (PM1, PM2, SBP, FBP, MK1, MK2,IMA, ISA, PC1, PC2) that acquire state quantities to be used in thecontrol of the electric motors MT1, MT2.

The suitability determining block HNT is configured of an initialdiagnosis block CHK and an actuation monitoring block MNT. In theinitial diagnosis block CHK, an initial diagnosis (a so-called initialcheck) before the actuation of the braking control device is started isexecuted. Further, in the actuation monitoring block MNT, actuation ofthe overall system is monitored at all times. A signal Shn indicatingthe suitability of the actuation states is outputted from thesuitability determining block HNT to the electromagnetic valvecontrolling part CSL (electromagnetic valve instructing block SOL).Information on which one of the first and second electric motors MT1,MT2 (that is, the first and second pressure-regulating mechanisms CA1,CA2) is in the suitable state and which one is in the unsuitable stateis conveyed to the electromagnetic valve controlling part CSL by thedetermination signal Shn.

In the initial diagnosis block CHK, diagnoses on the power supply stateto the braking control device, diagnosis of the electronic control unitECU (for example, memory diagnosis), the first and second electricmotors MT1, MT2, bridge circuit elements SWA to SWF, an electricconduction amount acquiring means IMA for the electric motors, first andsecond rotation angle acquiring means MK1, MK2, the electromagneticvalves VSM, VM1, VM2, VRN, an electric conduction amount acquiring meansISA for the electromagnetic valves, the braking operation volumeacquiring means BPA (SBP, etc.), and the fluid pressure acquiring meansPM1, PM2, PC1, PC2 (actuation check) are executed. Specifically, at atimepoint when the voltage supplied to the electronic control unit ECUshifts from a state of being less than a prescribed voltage v10 to astate of being equal to or greater than the prescribed voltage v10, atleast one actuation diagnosis (initial check) is executed from among therespective functions as above based on a trigger signal for the initialdiagnosis. A timepoint when the supplied voltage in the electroniccontrol unit ECU shifts from being less than a value v10 to a state ofbeing equal to or greater than the value v10 is termed “uponactivation”. For example, the trigger signal is determined based onsignals received from a communication bus CAN.

In the initial diagnosis block CHK, the initial actuation diagnosis isstarted at a timepoint after the activation of the electronic controlunit ECU and when the trigger signal is received. A state in which thetrigger signal is received is at least one of a state in which a driveris approaching the vehicle, a state where a vehicle door was opened andthen closed, a state where the driver sits on a vehicle seat, a statewhere an ignition switch is turned on, and a state in which the vehicleis running Thus, these states are determined based on at least one of anapproaching signal from an electronic key in a smart entry, anopen/close signal from the vehicle door, a seating signal for thevehicle seat, an on signal of the ignition switch, and a vehicle speed.Here, the smart entry is a function of a vehicle capable of locking andopening the vehicle door and the like and engine ignition without theuse of a mechanical key. In the smart entry, communication is executedbetween a key (portable device) possessed by the driver and anelectronic control unit (computer) installed in the vehicle, and thelocking or opening of the door is performed when the communication isestablished.

In the initial diagnosis (initial check), a diagnosis signal is sentfrom the initial diagnosis block CHK to the bridge circuits and therespective electromagnetic valves. Then, as a result of this, at leastone change in acquisition results of the electric conduction amountacquiring means IMA, ISA, the rotation angle acquiring means MK1, MK2,and the fluid pressure acquiring means PM1, PM2, PC1, PC2 (detectionresults of the respective sensors) is received by the initial diagnosisblock CHK. Based on this received result, whether or not the functionsof the bridge circuits (that is, the switching elements), the electricmotors MT1, MT2, the electromagnetic valves VSM, VM1, VM2, VRN, theelectric conduction amount acquiring means IMA, ISA, the rotation angleacquiring means MK1, MK2, and the fluid pressure acquiring means PM1,PM2, PC1, PC2 are in a state capable of normal actuation (suitablestate) or not (unsuitable state) is diagnosed. If there is a dysfunctionamong the functions (actuation thereof), a notification signal Huc issent from the suitability determining block HNT to a notification meansHUC, and notification to the driver is carried out.

Similarly, in the actuation monitoring block MNT as well, whether or notthe functions of the bridge circuits (that is, the switching elements),the electric motors MT1, MT2, the electromagnetic valves VSM, VM1, VM2,VRN, the electric conduction amount acquiring means IMA, ISA, therotation angle acquiring means MK1, MK2, and the fluid pressureacquiring means PM1, PM2, PC1, PC2 are in the state capable of normallyactuating or not is diagnosed. In the diagnosis of these constituentelements, the determination of the suitability is executed based oncomparisons of target values of the electric motors MT1, MT2 and theelectromagnetic valves VSM, VM1, VM2, VRN (which are the instructionsignals in the case of the electromagnetic valves) and results thereof(actual values). Specifically, the suitable state is determined in acase where a deviation between the target value and the actual value isless than a preset prescribed value, and the unsuitable state isdetermined in a case where this deviation is equal to or greater thanthe prescribed value. In a case where an unsuitable state exists amongthe functions of the respective constituent elements (MT1, MT2, etc.),preset procedures (for example, notification to the driver) are carriedout similar to the calculation process for the initial diagnosis blockCHK.

<<Motor Controlling Part CMT>>

The motor controlling part CMT (which is a part of the control meansCTL) is configured of an instruction fluid pressure calculating blockPWS, a target fluid pressure calculating block PWT, an instructionelectric conduction amount calculating block IST, a fluid pressurefeedback controlling block PFB, and a target electric conduction amountcalculating block IMT.

In the instruction fluid pressure calculating block PWS, first andsecond instruction fluid pressures Ps1, Ps2 are calculated based on thebraking operation volume Bpa and a calculation characteristic(calculation map) CHpw. Here, the first and second instruction fluidpressures Ps1, Ps2 are target values of the brake fluid pressure to begenerated by the first and second pressure-regulating mechanisms CA1,CA2. Specifically, the first and second instruction fluid pressures Ps1,Ps2 are calculated as zero in a range where the braking operation volumeBpa is equal to or greater than zero (corresponding to a case where thebraking operation is not performed) and less than a prescribed value bp0in the calculation characteristic CHpw, and the first and secondinstruction fluid pressures Ps1, Ps2 are calculated to increase fromzero according to the increase of the operation volume Bpa when theoperation volume Bpa is equal to or greater than the prescribed valuebp0.

In the target fluid pressure calculating block PWT, the first and secondinstruction fluid pressures Ps1, Ps2 are modified, and final targetvalues Pt1, Pt2 for the brake fluid pressure for the first and secondpressure-regulating mechanisms CA1, CA2 are calculated. Specifically,the target fluid pressure calculating block PWT includes ananti-skidding controlling block ABS, a traction controlling block TCS,and a vehicle stabilization controlling block ESC, and first and secondtarget fluid pressures Pt1, Pt2 required for executing the anti-skiddingcontrol, the traction control, and the vehicle stabilization control arecalculated. Accordingly, there may be a case where values of the firsttarget fluid pressure Pt1 and the second target fluid pressure Pt2differ. In a case where the execution of the anti-skidding control, thetraction control, and the vehicle stabilization control is not required,the first and second instruction fluid pressures Ps1, Ps2 are notmodified and are outputted as they are as the first and second targetfluid pressures Pt1, Pt2 from the target fluid pressure calculatingblock PWT.

In the anti-skidding controlling block ABS, the first and second targetfluid pressures Pt1, Pt2 for executing the anti-skidding control toprevent wheel locking are calculated based on an acquired result (wheelspeed Vwa) from a wheel speed acquiring means VWA provided on eachwheel. Specifically, in the anti-skidding controlling block ABS, wheelslip state quantities Slp (variants indicating state of decelerationslip of the wheels) are calculated based on the acquired results (wheelspeeds Vwa) from the wheel speed acquiring means VWA provided on therespective wheels. In the anti-skidding controlling block ABS, the firstand second instruction fluid pressures Ps1, Ps2 are modified based onthe wheel slip state quantities Slp and the first and second targetfluid pressures Pt1, Pt2 are determined thereby.

Similarly, in the traction controlling block TCS, the first and secondtarget fluid pressures Pt1, Pt2 for executing the traction control tosuppress wheel spin (over rotation) are calculated based on the acquiredresult (wheel speed Vwa) from the wheel speed acquiring means VWA.Specifically, the first and second target fluid pressures Pt1, Pt2 aredetermined based on the wheel slip state quantities Slp (the variantsindicating the state of deceleration slip of the wheels).

Moreover, in the vehicle stabilization controlling block ESC, the firstand second target fluid pressures Pt1, Pt2 for executing the vehiclestabilization control are calculated based on acquired results (steeringangle Saa, yaw rate Yra, lateral acceleration Gya) from a steering angleacquiring means SAA and a vehicle behavior acquiring means (yaw ratesensor YRA, lateral acceleration sensor GYA). Specifically, the firstand second instruction fluid pressures Ps1, Ps2 are modified to suppressat least one of excessive understeering and oversteering of the vehiclebased on the steering angle Saa, the yaw rate Yra, and the lateralacceleration Gya, and the first and second target fluid pressures Pt1,Pt2 is determined thereby.

In the instruction electric conduction amount calculating block IST,instruction electric conduction amounts Is1, Is2 (target values of theelectric conduction amount for controlling MT1, MT2) for the first andsecond electric motors MT1, MT2 that drive the first and secondpressure-regulating mechanisms CA1, CA2 are calculated based on thefirst and second target fluid pressures Pt1, Pt2, etc. Here, the“electric conduction amount” is the state quantity (variant) forcontrolling the output torque of the first and second electric motorsMT1, MT2. Since the first and second electric motors MT1, MT2 output thetorque which substantially is proportional to current, current targetvalues to the electric motors MT1, MT2 are used as the target values ofthe electric conduction amounts (target electric conduction amounts).Further, when the supplied voltages to the first and second electricmotors MT1, MT2 are increased, the current thereof is increased as aresult, so the supplied voltage values are used as the target electricconduction amounts. Moreover, since the supplied voltage values may beadjusted by duty ratio of pulse width modulation, this duty ratio (ratioof electrically conducted time period within a cycle) may be used as theelectric conduction amounts.

In the instruction electric conduction amount calculating block IST,signs (positive or negative sign for the values) of the first and secondinstruction electric conduction amounts Is1, Is2 are determined based ondirections toward which the first and second electric motors MT1, MT2should rotate (that is, increasing and decreasing directions of thefluid pressure). Further, magnitudes of the first and second instructionelectric conduction amounts Is1, Is2 are calculated based on therotational power (that is, increasing and decreasing amounts of thefluid pressure) that the first and second electric motors MT1, MT2should output. Specifically, in a case of increasing the brake fluidpressure, the signs of the first and second instruction electricconduction amounts Is1, Is2 are calculated as positive signs (Is1,Is2>0), and the first and second electric motors MT1, MT2 are driven inthe forward direction Fwd. On the other hand, in a case of decreasingthe brake fluid pressure, the signs of the first and second instructionelectric conduction amounts Is1, Is2 are determined as negative signs(Is1, Is2<0), and the first and second electric motors MT1, MT2 aredriven in the reverse direction Rvs. Moreover, the output torque(rotational power) of the first and second electric motors MT1, MT2 iscontrolled to be larger with larger absolute values of the first andsecond instruction electric conduction amounts Is1, Is2, and the outputtorque is controlled to be smaller for smaller absolute values of It1,It2.

In the fluid pressure feedback controlling block PFB, feedback electricconduction amounts Ib1, Ib2 of the first and second electric motors MT1,MT2 are calculated based on the first and second target values (targetfluid pressures) Pt1, Pt2 of the fluid pressure and the first and secondactual values Pc1, Pc2 of the fluid pressure. Here, the first and secondactual values Pc1, Pc2 are actual values of the fluid pressure (actualfluid pressures) acquired (detected) by the control cylinder fluidpressure acquiring means (pressure sensors) PC1, PC2. In the fluidpressure feedback controlling block PFB, deviations eP1, eP2 of thefirst and second target fluid pressures Pt1, Pt2 and the first andsecond actual fluid pressures Pc1, Pc2 are calculated. The fluidpressure deviations eP1, eP2 are subjected to differential and integralcalculations and gains Kp, Kd, Ki are multiplied thereto, as a result ofwhich the first and second feedback electric conduction amounts Ib1, Ib2are calculated. In the fluid pressure feedback controlling block PFB, aso-called fluid pressure-based PID control is executed.

In the target electric conduction amount calculating block IMT, thefirst and second target electric conduction amounts It1, It2, which arethe final target values of the electric conduction amounts arecalculated based on the first and second instruction electric conductionamounts Is1, Is2 and the first and second feedback electric conductionamounts Ib1, Ib2. Specifically, in the electric conduction amountadjustment calculating block IMT, the first and second feedback electricconduction amounts Ib1, Ib2 are added to the first and secondinstruction electric conduction amounts Is1, Is2, and sums thereof arecalculated as the first and second target electric conduction amountsIt1, It2 (It1=Is1+Ib1, It2=Is2+Ib2).

In the electric motor driving means (driving circuit) DRM, therotational power (outputs) of the first and second electric motors MT1,MT2 and the rotation directions thereof are adjusted based on the firstand second target electric conduction amounts It1, It2. Details of thedriving means DRM will be described later.

<<Electromagnetic Valve Controlling Part CSL>>

The electromagnetic valve controlling part CSL (which is a part of thecontrol means CTL) is configured of an electromagnetic valve instructingblock SOL and an electromagnetic valve driving means DRS. In theelectromagnetic valve instructing block SOL, instruction signals Vsm,Vm1, Vm2, Vrn of the electromagnetic valves VSM, VM1, VM2, VRN arecalculated based on the braking operation volume Bpa and thedetermination signal Shn indicating the suitability state. In theelectromagnetic valve driving means DRS, the flowing states (openpositions) and the interrupted states (closed positions) of theelectromagnetic valves VSM, VM1, VM2, VRN are selectively produced(controlled) based on the instruction signals Vsm, Vm1, Vm2, Vrn.

In the electromagnetic valve instructing block SOL, in a case where thesuitability determination signal Shn determines that “the entire systemis in the suitable state”, the states of electrical conduction ornon-conduction of the respective electromagnetic valves (VSM, etc.) arecontrolled based on the braking operation volume Bpa. Firstly, theoccurrence of the braking operation by the driver is determined based onthe operation volume Bpa. Specifically, “braking operation occurring(the braking operation is being performed)” is determined in a casewhere the operation volume Bpa is equal to or greater than theprescribed value bp0, and “no braking operation (the braking operationis not performed)” is determined in a case where the operation volumeBpa is less than the prescribed value bp0.

In the electromagnetic valve instructing block SOL, in a case where thecondition “braking operation occurring (that is, Bpa≤bp0)” is satisfied,the instruction signals Vsm, Vm1, Vm2 are sent to the electromagneticvalve driving means DRS so that the driving states of theelectromagnetic valves VSM, VM1, VM2 are switched from non-conductedstate to conducted state. Further, in the electromagnetic valveinstructing block SOL, an instruction signal Vrn for the electromagneticvalve VRN is created and is sent to the driving means DRS.

In the electromagnetic valve driving means DRS, the open/close states ofthe electromagnetic valves VSM, VM1, VM2, VRN are switched based on theinstruction signals Vsm, Vm1, Vm2, Vrn. Further, the electromagneticvalve electric conduction amount acquiring means (current sensor) ISAfor acquiring the electric conduction amounts Isa to the electromagneticvalves VSM, VM1, VM2, VRN is provided in the driving means DRS. Drivingmethods for the first and second master cylinder shutoff valves VM1, VM2and the electromagnetic valve VRN will be described later.

In the electronic control unit ECU as well, the power is supplied fromthe power source (BAT, etc.) and the functions thereof are therebyexecuted. Due to this, in a case where the power source is failing (thatis, the supplied power is insufficient), the ECU itself does notfunction, and the power supply to the electric motors MT1, MT2 and theelectromagnetic valves VSM, VM1, VM2, VRN may not be carried out. Due tothis, as the electromagnetic valves VSM, VRN, normally-closedelectromagnetic valves (NC valves) are employed, and normally-openelectromagnetic valves (NO valves) are employed as the electromagneticvalves VM1, VM2. As a result, in the case where the power source is inthe unsuitable state, the connection between the master cylinder MCL andthe simulator SSM is interrupted, and the connections between the mastercylinder MCL and the wheel cylinders (WCfl, War, etc.) may be ensured.

<Example of Electric Motor Driving Means DRM (Example of Three-PhaseBrushless Motor)>

FIG. 4 is an example of the driving means (driving circuit) DRM for acase where the first electric motor MT1 is a brushless motor. Theelectric motor driving means DRM is an electric circuit that drives thefirst electric motor MT1, and is configured of the bridge circuitconfigured of six switching elements SWA to SWF, a pulse widthmodulating block PWM configured to execute pulse width modulation basedon the first target electric conduction amount It1, a switchingcontrolling block SWT configured to control electricity-suppliedstates/non-electricity-supplied states of SWA to SWF based on a firstduty ratio Du1 determined by PWM, and the electric conduction amountacquiring means IMA.

The six switching elements SWA to SWF are elements capable of turningon/off parts of the electric circuit, and for example, MOS-FETs can beused. In the brushless motor, a first position acquiring means MK1acquires a rotor position (rotation angle) Mk1 of the first electricmotor MT1. Further, with the switching elements SWA to SWF configuringthe bridge circuit (three-phase bridge circuit) being controlled,directions of coil conduction amounts (that is, excitation directions)of a U phase (Tu terminal), a V phase (Tv terminal), and a W phase (Twterminal) are switched sequentially based on the first rotation angleMk1, and the first electric motor MT1 is thereby rotary driven. That is,the rotation direction of the brushless motor (forward direction Fwd orreverse direction Rvs) is determined according to a relationship of therotor and positions of excitation. Here, the forward direction Fwd ofthe first electric motor MT1 is a rotary direction corresponding to theincrease of the brake fluid pressure, and the reverse direction Rvs ofthe first electric motor MT1 is a rotary direction corresponding to thedecrease of the brake fluid pressure.

In the pulse width modulating block PWM, instruction value (targetvalue) for executing the pulse width modulation for each switchingelement is calculated based on the first target electric conductionamount It1. A pulse width duty ratio (ratio of on-time period within acycle) is determined based on a magnitude of the first target electricconduction amount It1 and a preset characteristic (calculation map).Together with this, the rotary direction of the first electric motor MT1is determined based on the sign of the first target electric conductionamount It1 (being positive or negative sign). For example, the rotarydirection of the first electric motor MT1 is set as that the forwarddirection Fwd is the positive (plus) value and the reverse direction Rvsis the negative (minus) value. Since the final output voltage isdetermined according to the input voltage (voltage of the battery BAT)and the first duty ratio Du1, the rotary direction and the output torqueof the first electric motor MT1 is thereby controlled.

In the switching controlling block SWT, driving signals Sa to Sf forsetting the respective switching elements configuring the bridge circuitin the on-state (electricity-supplied state) or off-state(non-electricity-supplied state) are calculated based on the first dutyratio (target value) Du1. By these driving signals Sa to Sf, theconduction and non-conduction states of the switching elements SWA toSWF are controlled. Specifically, conduction time per unit time in theswitching elements are set longer for larger first duty ratio Du1,resulting in larger current being supplied to the first electric motorMT1, and the output (rotational power) thereof becomes larger.

The electric conduction amount acquiring means (for example, currentsensor) IMA is provided in the electric motor driving means DRM, and theactual electric conduction amount (for example, actual current value)Ima is acquired (detected). Further, in the switching controlling blockSWT, a so-called current feedback control is executed. The first dutyratio Du1 is modified (finely adjusted) based on the deviation ΔImbetween the actual electric conduction amount Ima and the first targetelectric conduction amount It1. Highly accurate motor control can beachieved by this current feedback control.

<First Example of Brake Fluid Initial Filling Control>

A processing example of the control means CTL (motor controlling partCMT and electromagnetic valve controlling part CSL) will be described indetail with reference to a flow chart of FIG. 5. Here, a process for acase where one of the first and second pressure-regulating mechanismsCA1, CA2 fails and the other thereof is normal will be termed “brakefluid initial filling control”.

In a first example of the brake fluid initial filling control, firstlyin step S400, the braking operation volume Bpa and the determinationsignal Shn are read. Next, the process proceeds to step S410.

In step S410, a determination is made on whether “braking or not” basedon the braking operation volume Bpa. Specifically, it is determined as“braking” in a case where the braking operation volume Bpa is equal toor greater than the prescribed value bp0. Further, it is determined as“not braking (non-braking)” in a case where the braking operation volumeBpa is less than the prescribed value bp0. In the case where “braking”is affirmed in step S410 (case of “YES”), the process proceeds to stepS420. On the other hand, in the case where “braking” is denied in stepS410 (that is, non-braking in the case of “NO”), the process returns tostep S400.

In step S420, a determination is made on whether “the firstpressure-regulating mechanism CA1 is in the suitable state or not” basedon the determination signal Shn. Here, the determination signal Shn isthe signal indicating the suitability of the actuation of the first andsecond pressure-regulating mechanisms CA1, CA2 calculated in thesuitability determining block HNT (see FIG. 3). In a case where “thefirst pressure-regulating mechanism CA1 being in the suitable state” isaffirmed in step S420 (in the case of “YES”), the process proceeds tostep S430. On the other hand, in a case where “the firstpressure-regulating mechanism CA1 being in the suitable state” is deniedin step S420 (that is, in the unsuitable state and in the case of “NO”),the process proceeds to step S440.

In step S430, a determination is made on whether “the secondpressure-regulating mechanism CA2 is in the suitable state or not” basedon the determination signal Shn. In a case where “the secondpressure-regulating mechanism CA2 being in the suitable state” isaffirmed in step S430 (in the case of “YES”), the process proceeds tostep S470. On the other hand, in a case where “the secondpressure-regulating mechanism CA2 being in the suitable state” is deniedin step S430 (that is, in the unsuitable state and in the case of “NO”),the process proceeds to step S450.

In step S440, a determination is made on whether “the secondpressure-regulating mechanism CA2 is in the suitable state or not” basedon the determination signal Shn. In a case where “the secondpressure-regulating mechanism CA2 being in the suitable state” isaffirmed in step S440 (in the case of “YES”), the process proceeds tostep S460. On the other hand, in a case where “the secondpressure-regulating mechanism CA2 being in the suitable state” is deniedin step S440 (that is, in the unsuitable state and in the case of “NO”),the process proceeds to step S570.

In step S450, a determination is made on whether “the braking operationvolume Bpa is less than the prescribed value bpk or not” based on thebraking operation volume Bpa. In a case where “the braking operationvolume Bpa being less than the prescribed value bpk” is affirmed in stepS450 (in the case of “YES”), the process proceeds to step S490. On theother hand, in a case where “the braking operation volume Bpa being lessthan the prescribed value bpk” is denied in step S450 (that is, in theunsuitable state and in the case of “NO”), the process proceeds to stepS510.

In step S460, a determination is made on whether “the braking operationvolume Bpa is less than the prescribed value bpk or not” based on thebraking operation volume Bpa. In a case where “the braking operationvolume Bpa being less than the prescribed value bpk” is affirmed in stepS460 (in the case of “YES”), the process proceeds to step S530. On theother hand, in a case where “the braking operation volume Bpa being lessthan the prescribed value bpk” is denied in step S460 (that is, in theunsuitable state and in the case of “NO”), the process proceeds to stepS550.

In step S470, the connection valve VRN (corresponding to thirdopening/closing means) is brought to the closed position and the firstand second master cylinder shutoff valves VM1 (corresponding to firstopening/closing means), VM2 (corresponding to second opening/closingmeans) are brought to the closed positions. Specifically, theelectromagnetic valves VRN, VM1, VM2 brought to the non-flowing statesbased on the instruction signals Vrn, Vm1, Vm2 sent to the driving meansDRS. After this, the process proceeds to step S480.

In step S480, the wheel cylinders WCfl (corresponding to first wheelcylinder WC1), WCrr are pressurized by the first pressure-regulatingmechanism CA1, and the wheel cylinders WCfr (corresponding to secondwheel cylinder WC2), WCrl are pressurized by the secondpressure-regulating mechanism CA2. After this, the process returns tostep S400.

In step S490, the connection valve VRN and the first master cylindershutoff valve VM1 are brought to the closed positions and the secondmaster cylinder shutoff valve VM2 is brought to the open position.Specifically, the electromagnetic valves VRN, VM1 are brought to thenon-flowing state and the electromagnetic valve VM2 is brought to theflowing state based on the instruction signals Vrn, Vm1, Vm2 sent to thedriving means DRS. After this, the process proceeds to step S500.

In step S500, the wheel cylinders WCfl, WCrr are pressurized by thefirst pressure-regulating mechanism CA1, and the wheel cylinders WCfr,WCrl are pressurized by the master cylinder MCL. After this, the processreturns to step S400.

In step S510, the connection valve VRN is brought to the open positionand the first and second master cylinder shutoff valves VM1, VM2 arebrought to the closed positions. Specifically, the electromagnetic valveVRN is brought to the flowing state and the electromagnetic valves VM1,VM2 are brought to the non-flowing states based on the instructionsignals Vrn, Vm1, Vm2 sent to the driving means DRS. After this, theprocess proceeds to step S520.

In step S520, all the wheel cylinders WCfl, WCrr, WCfr, WCrl arepressurized by the first pressure-regulating mechanism CA1. After this,the process returns to step S400.

In step S530, the connection valve VRN and the second master cylindershutoff valve VM2 are brought to the closed positions and the firstmaster cylinder shutoff valve VM1 is brought to the open position.Specifically, the electromagnetic valves VRN, VM2 are brought to thenon-flowing states and the electromagnetic valve VM1 is brought to theflowing state based on the instruction signals Vrn, Vm1, Vm2 sent to thedriving means DRS. After this, the process proceeds to step S540.

In step S540, the wheel cylinders WCfl, WCrr are pressurized by themaster cylinder MCL, and the wheel cylinder WCfr, WCrl are pressurizedby the second pressure-regulating mechanism CA2. After this, the processreturns to step S400.

In step S550, the connection valve VRN is brought to the open positionand the first and second master cylinder shutoff valves VM1, VM2 arebrought to the closed positions. Specifically, the electromagnetic valveVRN is brought to the flowing state and the electromagnetic valves VM1,VM2 are brought to the non-flowing states based on the instructionsignals Vrn, Vm1, Vm2 sent to the driving means DRS. After this, theprocess proceeds to step S520.

In step S560, all the wheel cylinders WCfl, WCrr, WCfr, WCrl arepressurized by the second pressure-regulating mechanism CA2. After this,the process returns to step S400.

In step S570, the connection valve VRN is brought to the closed positionand the first and second master cylinder shutoff valves VM1, VM2 arebrought to the open positions. Specifically, including a case where thepower failed, the electromagnetic valve VRN is brought to thenon-flowing state and the electromagnetic valves VM1, VM2 are brought tothe flowing state based on the instruction signals Vrn, Vm1, Vm2 sent tothe driving means DRS. After this, the process proceeds to step S580.

In step S580, all the wheel cylinders WCfl, WCrr, WCfr, WCrl arepressurized by the master cylinder MCL. After this, the process returnsto step S400.

As described above, in the case where both the first and secondpressure-regulating mechanisms CA1, CA2 are actuating normally, the twobraking systems (first and second fluid paths H1, H2) are in independentstates by having the connection valve VRN in the closed position.Further, when the first and second master cylinder shutoff valves VM1,VM2 are brought to the closed positions, the master cylinder MCL and allthe wheel cylinders come to be in the hydrodynamically interruptedstate. Then, the wheel cylinders WCfl, WCrr connected to the first fluidpath H1 are pressurized by the first pressure-regulating mechanism CA1and the wheel cylinders WCfr, WCrl connected to the second fluid path H2are pressurized by the second pressure-regulating mechanism CA2. At thisoccasion, the simulator shutoff valve VSM is brought to the openposition and the master cylinder MCL is brought to the flowing statewith the simulator SSM.

In the case where both the first and second pressure-regulatingmechanisms CA1, CA2 are failing, including the case of power failure,the connection valve VRN is brought to the closed position and the firstand second master cylinder shutoff valves VM1, VM2 are brought to theopen positions. Due to this, all the wheel cylinders are pressurized bythe master cylinder MCL. At this occasion, the simulator shutoff valveVSM is brought to the closed position and the master cylinder MCL isbrought to the non-flowing state with the simulator SSM.

In the case where one of the first and second pressure-regulatingmechanisms CA1, CA2 fails and the other thereof is normal, thepressurization of the wheel cylinders (initial filling control of brakefluid) is executed according to the following two patterns based on thebraking operation volume Bpa.

In the case where the braking operation volume Bpa is less than theprescribed value bpk (that is, in an initial stage of the brakingoperation), the connection valve VRN is brought to the closed positionand the two brake systems H1, H2 are hydrodynamically separated andindependent. The wheel cylinders on the fluid path connected to thenormal pressure-regulating mechanism are pressurized by thispressure-regulating mechanism. On the other hand, the wheel cylinders onthe fluid path connected to the dysfunctioning pressure-regulatingmechanism are pressurized by the master cylinder MCL. In the initialstage of the braking operation, some brake fluid volume is initiallynecessary to fill a gap between the frictional member (brake pad) andthe rotary member (brake disk). At this occasion, the operational forceof the brake operation member BP is not so much required. The brakefluid is supplied from the master cylinder MCL to the wheel cylinders onthe fluid path connected to the failed pressure-regulating mechanism(initial filling). As a result, the brake fluid volume which the normalpressure-regulating mechanism can discharge can be saved.

At the timepoint when the braking operation volume Bpa becomes equal toor greater than the prescribed value bpk, the connection valve VRN isshifted from the closed position to the open position and the two brakesystems H1, H2 become hydrodynamically connected. The master cylindershutoff valve on the fluid path connected to the dysfunctioningpressure-regulating mechanism is shifted from the open position to theclosed position, so all the wheel cylinders (that is, the two brakesystems) are pressurized by the normal pressure-regulating mechanism. Inthe case of Bpa≥bpk, since the operational force of BP becomesnecessary, the pressurization is executed by the normalpressure-regulating mechanism without depending on the master cylinderMCL. Since the brake fluid is being fed from the master cylinder MCL tothe wheel cylinders connected to the dysfunctioning pressure-regulatingmechanism under the state of Bpa<bpk, the normal pressure-regulatingmechanism still has allowances to its dischargeable brake fluid volumeeven in a situation where the braking operation volume Bpa becomeslarge. As a result, bottoming of the pressure-regulating mechanism canbe suppressed.

<Workings and Effects of Brake Fluid Initial Filling Control of FirstExample>

Workings and effects of the brake fluid initial filling control of thefirst example will be described with reference to a characteristicsdiagram of FIG. 6. Here, the situation in which the firstpressure-regulating mechanism CA1 is in the dysfunctioning state and thesecond pressure-regulating mechanism CA2 is in the suitable state willbe assumed.

When the driver starts to operate BP, “braking operation occurring” isdetermined at the timepoint when the braking operation volume Bpa (forexample, the operational displacement Sbp) reaches the value bp0 (stepS410). Then, the determination is made on whether “the first and secondpressure-regulating mechanisms CA1, CA2 are in the suitable states ornot” is made based on the determination signal Shn from the suitabilitydetermining block HNT (steps S420 to S440). That is, “the firstpressure-regulating mechanism CA1 being in the dysfunctioning state andthe second pressure-regulating mechanism CA2 being in the suitablestate” is hereby determined.

At this timepoint, since the braking operation volume Bpa is less thanthe prescribed value bpk, the connection valve VRN is brought to theclosed position, the first master cylinder shutoff valve VM1 is broughtto the open position, and the second master cylinder shutoff valve VM2are brought to the closed position (step S530). In accordance with theincrease in the braking operation volume Bpa, the second fluid path H2(that is, the fluid pressure Pc2 in the second wheel cylinder) isincreased as shown by a broken line in the drawing by the normallyactuating second pressure-regulating mechanism CA2. On the other hand,the first fluid path H1 (that is, the fluid pressure Pc1 of the firstwheel cylinder) is increased by the master cylinder MCL toward a pointP. The simulator shutoff valve VSM is brought to the closed position sothat the brake fluid volume is not consumed by the stroke simulator SSM.

At the timepoint when the braking operation volume Bpa reaches theprescribed value bpk, the connection valve VRN is shifted from theclosed position to the open position and the first master cylindershutoff valve VM1 is shifted from the open position to the closedposition (step S550). Here, the second master cylinder shutoff valve VM2remains in the closed position. At this timepoint, the first fluid pathH1 and the second fluid path H2 come to be in the flowing states, andthe first wheel cylinder WC1 and the master cylinder MCL come to be inthe non-flowing states. As a result, the fluid pressures Pc1, Pc2 becomeequal, and are increased by the second pressure-regulating mechanism CA2in accordance with the increase in the braking operation volume Bpa.

In the relationships of the master cylinder, the wheel cylinder, thebrake caliper, the frictional member (brake pad), and the rotary member(brake disk), an operational force Fbp to the operational displacementSbp of the brake operation member BP (that is, a master cylinder fluidpressure) exhibits a characteristic of “protruding downward”. Thischaracteristic is due to the brake fluid volume (that is, theoperational displacement Sbp) filling the gap between the frictionalmember and the rotary member in the initial stage of the brakingoperation, and this deforms the ones among the respective members withlow rigidity. Due to this, in the brake system in which thepressure-regulating mechanism is dysfunctioning, the brake fluid issupplied from the master cylinder MCL while the braking operation volumeBpa is between the prescribed value bp0 to bpk. Then, at the timepointwhen the braking operation volume Bpa becomes the value bpk, the brakesystem in which the pressure-regulating mechanism is dysfunctioning isalso pressurized by the normally actuating pressure-regulatingmechanism. Due to this, the brake fluid volume that the normallyactuating pressure-regulating mechanism can discharge is ensured, andthe cylinder bottoming can be suppressed.

<Second Example of Brake Fluid Initial Filling Control>

A second example of the brake fluid initial filling control in thecontrol means CTL will be described in detail with reference to a flowchart of FIG. 7. In the second example, steps S490, S500, S530, S540 inthe first example differs therein. Thus, descriptions related to othersteps given the same reference signs will be omitted, and differingsteps will be described.

In step S600, the connection valve VRN is brought to the closed positionand the first and second master cylinder shutoff valves VM1, VM2 arebrought to the open positions. Specifically, the electromagnetic valveVRN is brought to the non-flowing state and the electromagnetic valvesVM1, VM2 are brought to the flowing states based on the instructionsignals Vrn, Vm1, Vm2 sent to the driving means DRS. After this, theprocess proceeds to step S610. Here, in step S600, the connection valveVRN may be brought to the open position.

In step S610, all the wheel cylinders WCfl, WCfr, WCrl, WCrr arepressurized by the master cylinder MCL. After this, the process returnsto step S400.

In step S620, the connection valve VRN is brought to the closed positionand the first and second master cylinder shutoff valves VM1, VM2 arebrought to the open positions. Specifically, the electromagnetic valveVRN is brought to the non-flowing state and the electromagnetic valvesVM1, VM2 are brought to the flowing states based on the instructionsignals Vrn, Vm1, Vm2 sent to the driving means DRS. After this, theprocess proceeds to step S630. Here, in step S620, the connection valveVRN may be brought to the open position.

In step S630, all the wheel cylinders WCfl, WCfr, WCrl, WCrr arepressurized by the master cylinder MCL. After this, the process returnsto step S400.

As described above, the cases where the second example of the brakefluid initial filling control differs from the first example are thecase where one of the first and second pressure-regulating mechanismsCA1, CA2 fails and the other thereof is normal, and the case where thebraking operation volume Bpa is less than the prescribed value bpk. Inthe first example, the wheel cylinders on the failed side arepressurized by the master cylinder MCL and the wheel cylinders on theother normal side are pressurized by the pressure-regulating mechanism.On the other hand, in the second example, all the wheel cylinders arepressurized by the master cylinder MCL. However, since the brake fluidis supplied to the wheel cylinders from the master cylinder MCL in theinitial stage of the braking operation, the brake fluid volume which thenormal pressure-regulating mechanism can discharge can be saved, similarto the first example.

<Workings and Effects of Brake Fluid Initial Filling Control of SecondExample>

Workings and effects of the brake fluid initial filling control of thesecond example will be described with reference to a characteristicsdiagram of FIG. 8. Here, similar to the first example, the situation inwhich the first pressure-regulating mechanism CA1 is in thedysfunctioning state and the second pressure-regulating mechanism CA2 isin the suitable state will be assumed.

When the driver starts to operate BP, “braking operation occurring” isdetermined at the timepoint when the braking operation volume Bpa (forexample, the operational displacement Sbp) reaches the value bp0. In theseries of subsequent steps, the determination is made on whether “thefirst and second pressure-regulating mechanisms CA1, CA2 are in thesuitable states or not” is made based on the determination signal Shn.At the timepoint when the series of processes are completed, “the firstpressure-regulating mechanism CA1 being in the dysfunctioning state andthe second pressure-regulating mechanism CA2 being in the suitablestate” is hereby determined.

At the timepoint of the above determination, since the braking operationvolume Bpa is less than the prescribed value bpk, the connection valveVRN is brought to the closed position (or the open position) and thefirst and second master cylinder shutoff valves VM1, VM2 are brought tothe open positions (step S620). In accordance with the increase in thebraking operation volume Bpa, the first fluid path H1 (that is, thefluid pressure Pc1 in the first wheel cylinder) and the second fluidpath H2 (that is, the fluid pressure Pc2 in the second wheel cylinder)are increased toward a point R by the master cylinder MCL (step S630.)Here, the simulator shutoff valve VSM is brought to the closed positionso that the brake fluid volume is not consumed by the stroke simulatorSSM.

At the timepoint when the braking operation volume Bpa reaches theprescribed value bpk, the first master cylinder shutoff valve VM1 isshifted from the open position to the closed position (step S550). Atthis timepoint, the connection valve VRN is in the open position, andthe second master cylinder shutoff valve VM2 is in the closed position.The first fluid path H1 and the second fluid path H2 come to be in theflowing states, and the first wheel cylinder WC1 and the master cylinderMCL come to be in the non-flowing states. The fluid pressures Pc1, Pc2are increased by the second pressure-regulating mechanism CA2 inaccordance with the increase in the braking operation volume Bpa. Here,the simulator shutoff valve VSM is brought to the open position.

The operational force Fbp to the operational displacement Sbp of thebrake operation member BP (that is, a master cylinder fluid pressure)exhibits the characteristic of “protruding downward”, and this is usedto fill the gap between the frictional member and the rotary member bythe brake fluid volume (that is, the operational displacement Sbp) inthe initial stage of the braking operation, and to deform the ones amongthe respective members with low rigidity. In the second example, thebrake fluid is supplied from the master cylinder MCL to all the wheelcylinders at the start of the braking operation, however, theoperational force thereof is small.

Similar to the first example, since the brake fluid is supplied to thewheel cylinders from the master cylinder MCL in the initial stage of thebraking operation, the brake fluid volume which the normalpressure-regulating mechanism can discharge achieves allowances, and thebottoming of the pressure-regulating mechanism can be suppressed.Further, in the second example, since all the wheel cylinders arepressurized by the master cylinder in the braking initial stage, a fluidpressure difference between the wheel cylinders WCfl, WCrr belonging tothe first fluid path H1 and the wheel cylinders WCfr, WCrl belonging tothe second fluid path H2 can be suppressed.

<Second Embodiment of Braking Control Device According to the PresentInvention>

Next, a second embodiment of the present invention will be describedwith reference to an overall configurational diagram of FIG. 9. In thefirst embodiment (see FIG. 1), the four wheel cylinders WCfl, WCfr,WCrl, WCrr are pressurized by the pressure-regulating mechanisms CA1,CA2, however, in the second embodiment, the front wheel cylinders WCfl,WCfr are pressurized by the pressure-regulating mechanisms CA1, CA2 andthe brake torque is applied thereto. Further, the rear wheels WHrl, WHrrare given the brake torque by electric braking means DSrl, DSrr that donot use fluid. Thus, the wheel cylinders WCrl, WCrr do not exist for therear wheels WHrl, WHrr, and the fluid pipe from the master cylinder MCLto the rear wheel cylinders WCrl, WCrr also does not exist. That is,fluid paths (piping), electromagnetic valves, and wheel cylinderscorresponding to the rear wheel do not exist.

In the respective drawings and descriptions using the same, similar tothe above, the members (constituent features) given the same referencesigns such as MCL, etc., exhibit the same function. In addition, similarto the above, the letters added to the end of the signs of therespective constituent features indicate which one of the four wheelscorresponds. Specifically, the added letters indicate that “fl”indicates a “left front wheel”, “fr” indicates a “right front wheel”,“rl” indicates a “left rear wheel”, and “rr” indicates a “right rearwheel”.

Since the constituent features given the same reference signs are sameas those of the first embodiment, the description will be simplified bydescribing mainly of differing portions.

The master cylinder MCL (first master cylinder chamber Rm1) and the leftfront wheel cylinder WCfl (corresponding to first wheel cylinder WC1)are connected by the first fluid path H1. The first master cylindershutoff valve VM1 being a two-position electromagnetic valve isinterposed in the first fluid path H1. The first pressure-regulatingmechanism CA1 driven by the first electric motor MT1 is connected to thefirst fluid path H1 between the first master cylinder shutoff valve VM1and the left front wheel cylinder WCfl.

Further, the master cylinder MCL (second master cylinder chamber Rm2)and the right front wheel cylinder (corresponding to second wheelcylinder WC2) WCfr are connected by the second fluid path H2. The secondmaster cylinder shutoff valve VM2 being a two-position electromagneticvalve is interposed in the second fluid path H2. The secondpressure-regulating mechanism CA2 driven by the second electric motorMT2 is connected to the second fluid path H2 between the second mastercylinder shutoff valve VM2 and the right front wheel cylinder WCfr.Further, the master cylinder MCL is connected to the simulator SSM viathe simulator shutoff valve VSM being a two-position electromagneticvalve.

The first pressure-regulating mechanism CA1 and the secondpressure-regulating mechanism CA2 are hydrodynamically connected by theconnection fluid path (brake piping) HRN. Further, the connection valveVRN is interposed on the connection fluid path HRN (H3). In a statewhere the connection valve VRN is in the open position, the connectionfluid path HRN is in a flowing state, and when it is in the closedposition, the connection fluid path HRN is in an interrupted state.

In the second embodiment as well, similar to the first embodiment, thefirst and second examples of the brake fluid initial filling control areapplied.

In the case where both the first and second pressure-regulatingmechanisms CA1, CA2 are actuating normally, the connection valve VRN isbrought to the interrupted state by the control means CTL (motorcontrolling part CMT and electromagnetic valve controlling part CSL),the first wheel cylinder WCfl is pressurized by the firstpressure-regulating mechanism CA1, and the second wheel cylinder WCfr ispressurized by the second pressure-regulating mechanism CA2.

In the case where both the first and second pressure-regulatingmechanisms CA1, CA2 are failing, the first and second master cylindershutoff valves VM1, VM2 are brought to the open positions, and the firstand second wheel cylinders WCfl, WCfr are pressurized by the mastercylinder MCL.

In the case where one of the first and second pressure-regulatingmechanisms CA1, CA2 fails and the other thereof is normal, the first andsecond wheel cylinders WCfl, WCfr are pressurized in two steps.

In the first example of the brake fluid initial filling control, onebrake system is pressurized by the master cylinder MCL and the otherbrake system is pressurized by the normal pressure-regulating mechanismin the initial stage of the braking operation (Bpa<bpk). At thetimepoint of having finished the initial stage of the braking operation(timepoint of satisfying Bpa≥bpk), the pressurization of the two brakesystems by the normal pressure-regulating mechanism is started.

In the initial stage of the braking operation, the operational force Fbpis not so much required, and only the operational displacement Sbp isrequired. Due to this, similar to the first embodiment, the secondembodiment also pressurizes the failed brake system by the mastercylinder MCL in the initial stage as above. As a result, the brake fluidvolume of the normal pressure-regulating mechanism is saved, and thedischargeable brake fluid volume can be increased.

In the second example of the brake fluid initial filling control, thetwo brake systems are pressurized by the master cylinder MCL in theinitial stage of the braking operation (Bpa<bpk). At the timepoint ofhaving finished the initial stage of the braking operation (timepoint ofsatisfying Bpa≥bpk), the pressurization of the two brake systems by thenormal pressure-regulating mechanism is started. Similarly, since thetwo brake systems are pressurized by the master cylinder MCL in theinitial stage of the braking, the braking fluid volume of the nominalpressure-regulating mechanism is saved, and the dischargeable brakefluid volume can be increased.

In the second embodiment, even if at least one of the first and secondpressure-regulating mechanisms CA1, CA2 is dysfunctioning, the braketorque can still be applied by the electric braking means DSrl, DSrrprovided on the rear wheels WHrl, WHrr, so the decelerated speed of thevehicle can be ensured.

<Electric Braking Means Provided on Rear Wheels in Second Embodiment>

The electric braking means provided on the rear wheels will be describedwith reference to a schematic diagram of FIG. 10, with the electricbraking means DSrl for the left rear wheel as an example. The electricbraking means DSrl is driven by an electric motor MTW (that is, thebrake torque of the rear wheel is adjusted). Here, the electric motorMTW is termed “wheel-side electric motor” to distinguish it from thefirst and second electric motors MT1, MT2 for driving the first andsecond pressure-regulating mechanisms CA1, CA2 provided on the vehiclebody side. Similar to the above, the constituent features given the samereference signs exhibit the same function, so the description thereofwill be omitted.

The vehicle is provided with the brake operation member BP, theelectronic control unit ECU and the electric braking means (brakeactuator) DSrl. The electronic control unit ECU and the electric brakingmeans DSrl are connected by a signal cable (signal line) SGL and a powercable (power line) PWL, and a driving signal and power for the electricmotor MTW dedicated to the electric braking means DSrl are therebysupplied.

In addition to the aforementioned suitability determining block HNT,etc., the electronic control unit ECU is provided with an instructionpressing force calculating block FBS. A target value (instructionpressing force) Fsrl for driving the electric motor MTW dedicated to theelectric braking means DSrl is calculated by the instruction pressingforce calculating block FBS. Specifically, in the instruction pressingforce calculating block FBS, the instruction pressing force Fsrl for theright rear wheel WHrl is calculated based on the braking operationvolume Bpa and a preset instruction pressing force calculationcharacteristic CHfb. The instruction pressing force Fsrl is a targetvalue of the pressing force, which is force for the frictional member(brake pad) MSB to press the rotary member (brake disk) KTrl in theelectric braking means DSrl for the right rear wheel. The instructionpressing force Fsrl is sent to DSrl on the wheel side through a serialcommunication bus SGL.

The electric braking means DSrl for the left rear wheel is configured ofthe brake caliper CPrl, a pressing piston PSW, the wheel-side electricmotor MTW, a rotation angle detecting means MKW, a reduction gear GSW,the output member OSF, the screw member NJW, a pressing force acquiringmeans FBA, and the drive circuit DRW.

The brake caliper CPrl is configured to interpose the rotary member(brake disk) KTrl therein via two frictional members (brake pads) MSB.The pressing piston (brake piston) PSW is slid within the caliper CPrl,and is reciprocated toward the rotary member KTrl. The pressing pistonPSW presses the frictional members MSB onto the rotary member KTrl togenerate frictional force. Since the rotary member KTrl is fixed to therear wheel WHrl, this frictional force adjusts the braking force on theleft rear wheel WHrl.

The wheel-side electric motor MTW for driving the electric braking meansDSrl generates electric power for pressing the frictional members MSBagainst the rotary member KTrl. Specifically, an output of the electricmotor MTW (rotational power about a motor axis) is transmitted to theoutput member OSF through the reduction gear GSW. Rotational power(torque about shaft axis) of the output member OSF is converted tolinear motion force (thrusting force in a direction of center axis ofPSW) by a motion converting member (for example, the screw member) NJW,and is transmitted to the pressing piston PSW.

The rotation angle acquiring means (for example, rotation angle sensor)MKW for the wheel-side electric motor MTW is provided. Further, thepressing force acquiring means FBA is provided in order to acquire(detect) a reaction force (reaction) of the force (pressing force) Fbaof the pressing piston PSW pressing the frictional member MSB. Further,a pressing force feedback control is executed based on the target valueFsrl and the actual value Fba of the pressing force.

The driving means (driving circuit) DRW drives the wheel-side electricmotor MTW based on the instruction pressing force (signal) Fsrl sentfrom the instruction pressing force calculating block FBS. Specifically,the driving means DRW is provided with the bridge circuit for drivingthe wheel-side electric motor MTW, and rotary direction and the outputtorque of the electric motor MTW are controlled by driving signals forrespective switching elements calculated based on the target value Fsrl.

As above, the electric braking device DSrl for the left rear wheel WHrlis described. Since the electric braking device DSrr for the right rearwheel WHrr is same as the electric braking device DSrl, the descriptionwill be omitted. The details of the electric braking device DSrr can bedescribed by replacing the added letter “rl” of the respective referencesigns to the added letter “rr”.

In the first embodiment, the first and second fluid pressure units HU1,HU2 are provided to allow the brake torque to be adjusted independentlyin each wheel in the anti-skidding control, etc.; however, in the secondembodiment, the first pressure-regulating mechanism CA1 can adjust thefluid pressure of the wheel cylinder WCfl independently from the fluidpressure adjustment of the wheel cylinder WCfr by the secondpressure-regulating mechanism CA2. Thus, in the second embodiment, thefirst and second fluid pressure units HU1, HU2 can be omitted.

1. A braking control device for a vehicle, the braking control devicecomprising: a master cylinder configured to be driven by a brakeoperation member of the vehicle; a first wheel cylinder configured toapply brake torque to one of left and right front wheels of the vehicle;a second wheel cylinder configured to apply brake torque to the other ofthe left and right front wheels of the vehicle; a first fluid pathconnecting the master cylinder and the first wheel cylinder; a secondfluid path connecting the master cylinder and the second wheel cylinder;a first opening/closing means provided on the first fluid path, andconfigured to selectively produce a flowing state and an interruptedstate of brake fluid between the master cylinder and the first wheelcylinder; a second opening/closing means provided on the second fluidpath, and configured to selectively produce a flowing state and aninterrupted state of brake fluid between the master cylinder and thesecond wheel cylinder; a third opening/closing means provided on aconnection fluid path connecting the first wheel cylinder and the secondwheel cylinder, and configured to selectively produce a flowing stateand an interrupted state of brake fluid between the first wheel cylinderand the second wheel cylinder; an operation volume acquiring meansconfigured to acquire an operation volume of the brake operation member;a first pressure-regulating mechanism connected to the first fluid pathbetween the first opening/closing means and the first wheel cylinder,and configured to pressurize the brake fluid in the first wheelcylinder; a second pressure-regulating mechanism connected to the secondfluid path between the second opening/closing means and the second wheelcylinder, and configured to pressurize the brake fluid in the secondwheel cylinder; a control means configured to control the first, second,and third opening/closing means and the first and secondpressure-regulating mechanisms based on the operation volume; and adetermination means configured to determine whether actuation of thefirst and second pressure-regulating mechanisms is in a suitable stateor in an unsuitable state, wherein in a case where the determinationmeans determines that the actuation of the first and secondpressure-regulating mechanisms is in the suitable state, the controlmeans causes the first, second, and third opening/closing means to be inthe interrupted state, and causes the brake fluid in the first wheelcylinder to be pressurized by the first pressure-regulating mechanismand the brake fluid in the second wheel cylinder to be pressurized bythe second pressure-regulating mechanism, and in a case where thedetermination means determines that the actuation of the firstpressure-regulating mechanism is in the unsuitable state and theactuation of the second pressure-regulating mechanism is in the suitablestate, the control means: causes the first opening/closing means to bein the flowing state and the second and third opening/closing means tobe in the interrupted state, and causes the brake fluid in the firstwheel cylinder to be pressurized by the master cylinder and the brakefluid in the second wheel cylinder to be pressurized by the secondpressure-regulating mechanism when the operation volume is less than aprescribed value, and causes the first opening/closing means to be inthe interrupted state and the third opening/closing means to be in theflowing state, and causes the brake fluid in the first and second wheelcylinders to be pressurized by the second pressure-regulating mechanismwhen the operation volume is equal to or more than the prescribed value.2. A braking control device for a vehicle, the braking control devicecomprising: a master cylinder configured to be driven by a brakeoperation member of the vehicle; a first wheel cylinder configured toapply brake torque to one of left and right front wheels of the vehicle;a second wheel cylinder configured to apply brake torque to the other ofthe left and right front wheels of the vehicle; a first fluid pathconnecting the master cylinder and the first wheel cylinder; a secondfluid path connecting the master cylinder and the second wheel cylinder;a first opening/closing means provided on the first fluid path, andconfigured to selectively producea flowing state and an interruptedstate of brake fluid between the master cylinder and the first wheelcylinder; a second opening/closing means provided on the second fluidpath, and configured to selectively produce a flowing state and aninterrupted state of brake fluid between the master cylinder and thesecond wheel cylinder; a third opening/closing means provided on aconnection fluid path connecting the first wheel cylinder and the secondwheel cylinder, and configured to selectively produce a flowing stateand an interrupted state of brake fluid between the first wheel cylinderand the second wheel cylinder; an operation volume acquiring meansconfigured to acquire an operation volume of the brake operation member;a first pressure-regulating mechanism connected to the first fluid pathbetween the first opening/closing means and the first wheel cylinder,and configured to pressurize the brake fluid in the first wheelcylinder; a second pressure-regulating mechanism connected to the secondfluid path between the second opening/closing means and the second wheelcylinder, and configured to pressurize the brake fluid in the secondwheel cylinder; a control means configured to control the first, second,and third opening/closing means and the first and secondpressure-regulating mechanisms based on the operation volume; and adetermination means configured to determine whether actuation of thefirst and second pressure-regulating mechanisms is in a suitable stateor in an unsuitable state, wherein in a case where the determinationmeans determines that the actuation of the first and secondpressure-regulating mechanisms is in the suitable state, the controlmeans causes the first, second, and third opening/closing means to be inthe interrupted state, and causes the brake fluid in the first wheelcylinder to be pressurized by the first pressure-regulating mechanismand the brake fluid in the second wheel cylinder to be pressurized bythe second pressure-regulating mechanism, and in a case where thedetermination means determines that the actuation of the firstpressure-regulating mechanism is in the unsuitable state and theactuation of the second pressure-regulating mechanism is in the suitablestate, the control means: causes the first and second opening/closingmeans to be in the flowing state, and causes the brake fluid in thefirst and second wheel cylinders to be pressurized by the mastercylinder when the operation volume is less than a prescribed value, andcauses the first and second opening/closing means to be in theinterrupted state and the third opening/closing means to be in theflowing state, and causes the brake fluid in the first and second wheelcylinders to be pressurized by the second pressure-regulating mechanismwhen the operation volume is equal to or more than the prescribed value.3. The braking control device for a vehicle according to claim 1,wherein the first pressure-regulating mechanism is configured of: afirst control cylinder including an first inner hole communicating withthe first fluid path; a first control piston fitted in the first innerhole of the first control cylinder in a fluid-tight manner and defininga control cylinder chamber communicating with the first fluid path inthe first inner hole; and a first electric motor configured toreciprocate the first control piston in an axial direction within thefirst inner hole to increase and decrease a volume of the controlcylinder chamber, and the second pressure-regulating mechanism isconfigured of: a second control cylinder including an second inner holecommunicating with the second fluid path; a second control piston fittedin the second inner hole of the second control cylinder in a fluid-tightmanner and defining a control cylinder chamber communicating with thesecond fluid path in the second inner hole; and a second electric motorconfigured to reciprocate the second control piston in an axialdirection within the second inner hole to increase and decrease a volumeof the control cylinder chamber.
 4. The braking control device for avehicle according to claim 2, wherein the first pressure-regulatingmechanism is configured of: a first control cylinder including an firstinner hole communicating with the first fluid path; a first controlpiston fitted in the first inner hole of the first control cylinder in afluid-tight manner and defining a control cylinder chamber communicatingwith the first fluid path in the first inner hole; and a first electricmotor configured to reciprocate the first control piston in an axialdirection within the first inner hole to increase and decrease a volumeof the control cylinder chamber, and the second pressure-regulatingmechanism is configured of: a second control cylinder including ansecond inner hole communicating with the second fluid path; a secondcontrol piston fitted in the second inner hole of the second controlcylinder in a fluid-tight manner and defining a control cylinder chambercommunicating with the second fluid path in the second inner hole; and asecond electric motor configured to reciprocate the second controlpiston in an axial direction within the second inner hole to increaseand decrease a volume of the control cylinder chamber.
 5. The brakingcontrol device for a vehicle according to claim 3, wherein thedetermination means determines whether actuation of each of the firstpressure-regulating mechanism and the second pressure-regulatingmechanism is in a suitable state or in an unsuitable state based on atleast one of an actuation state of an operation volume acquiring means,power supply states to the first electric motor and the second electricmotor, and an actuation state of the control means that drive controlsthe first electric motor and the second electric motor.
 6. The brakingcontrol device for a vehicle according to claim 4, wherein thedetermination means determines whether actuation of each of the firstpressure-regulating mechanism and the second pressure-regulatingmechanism is in a suitable state or in an unsuitable state based on atleast one of an actuation state of an operation volume acquiring means,power supply states to the first electric motor and the second electricmotor, and an actuation state of the control means that drive controlsthe first electric motor and the second electric motor.